That's bizarre on a few levels, but the obvious being that a straight person wouldn't assume a couple would accept a threesome with a strange person to join them
The two of you are a gorgeous, great couple together. Fucking sucking breeding. Would love to have the two of you daddies fuck my boy pussy. I'll bottom for both of you and both of you can blow your load deep inside of my pussy
Stayed in a motel once some years ago only to awaken at 3am hearing two men having sex in the adjacent room. Was tempted to call their room and ask if I could join in, but didn't. Saw them exit the room the next morning and was glad I didn't join in, let's just leave it at that.